1. Field of the Invention
The present invention relates to a safe method for removing halogenated aromatic compounds from hydrocarbon oil contaminated by halogenated aromatic compounds such as polychlorinated biphenyl (hereinafter "PCB"), using chemical reaction processing and extraction.
2. Description of Related Art
It is known that it is extremely difficult to treat hydrocarbon oil that during use has become contaminated by PCB or other such halogenated aromatic compound. This has led to considerable efforts directed toward the removal or decompsition of halogenated aromatic compounds. Methods for accomplishing this using a reaction process that takes place in the presence of an alkali include the alumina-alkali process disclosed by U.S. Pat. No. 2,951,804. U.S. Pat. No. 4,532,028 discloses a method of reacting alkali and a PCB content of up to 50,000 ppm in a mixture of alkyl or alkylene sulfoxide and polyole, thereby reducing the content to several ppm. Other examples include Canadian Patent No. 1,181,771 which discloses a method employing melted sodium, and Italian Patent No. 1,206,508 which discloses a method using alkaline earth metal on which PEG is adsorbed.
Each method has its good points and, in the case of non-aromatic hydrocarbon and other such samples containing high concentrations of halogenated aromatic compounds are recognized as being effective techniques for reducing concentrations of halogenated aromatic compounds to a low level.
However, with the prior art techniques it is not possible to further remove halogenated aromatic compounds from samples having a low concentration thereof, so that the halogenated aromatic compound content is further reduced to the extent that the inclusion thereof is substantially not recognizable; it is not yet possible to reduce the halogenated aromatic compound concentration to 1 ppm or below. Moreover, processes that are specifically for extracting contaminants having low concentration levels are considered very difficult. Also, it is widely known that heating the extraction solvent used in the prior art methods to a high temperature of 120.degree. C. or over in the presence of an alkali or alkali metal has a chemically destablizing effect that promotes solvent decomposition and polymerization, degrading the basic function of the extraction solvent.